There is a family of five members: K, L, M, N and O. Among them, there is one married couple. O is unmarried and is the brother of K. N is the sister of O. M is the only married female and the mother of N. L and O are the only males in the group. Who is the father of K?

Given information:

• Family of 5 members: K, L, M, N, and O
• One married couple exists
• O is unmarried and is the brother of K
• N is the sister of O
• M is the only married female and the mother of N
• L and O are the only males in the group

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Since L and O are the only males, the remaining members K, M, and N must be females.

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O is unmarried and is the only other male besides L.

Since there is one married couple and M is the only married female, the married couple must be M and L.

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M is the mother of N.

N is the sister of O, which means N and O are siblings with the same parents.

Therefore, M is also the mother of O.

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O is the brother of K, which means O and K are siblings with the same parents.

Since M is the mother of O, M is also the mother of K.

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Since M is the mother of K, N, and O, and L is married to M, L must be the father of all three children.

Therefore, the father of K is L.

The answer is Option 4: L